The invention relates to improvements in apparatus for damping vibrations, especially between the output element of an engine (such as the internal combustion engine of a motor vehicle) and a power train (particularly the power train including the change-speed transmission in a motor vehicle). More particularly, the invention relates to improvements in torsional vibration damping apparatus of the type wherein at least two flywheels are rotatable relative to each other against the opposition of damper means, wherein one of the flywheels is connectable to the output element of the engine, and wherein another flywheel is connectable with the input element of a change-speed transmission, especially by way of a clutch (such as a friction clutch).
Vibration damping apparatus of the above outlined character normally employ one or more dampers which comprise elastic energy storing elements (such as circumferentially extending coil springs) installed or operating between the flywheels in such a way that they oppose rotation of the flywheels relative to each other and undergo compression and store energy when one of the flywheels is caused to change its angular position with reference to the other flywheel, and/or energy storing elements which act in the axial direction and employ or cooperate with friction pads or linings to generate friction (i.e., hysteresis). As a rule, or in many instances, the energy storing elements which act in the axial direction of the flywheels are connected in parallel with the damper or dampers acting in the circumferential direction of the flywheels.
It has been found that, though the just described conventional vibration damping apparatus are quite satisfactory under certain operating conditions (i.e., they can damp certain types of vibrations and they can also reduce noise which develops in response to angular movements of the flywheels relative to each other), the operation of all presently known apparatus constitutes a compromise between an optimum operation under first circumstances and a less satisfactory operation under different second circumstances. For example, purely mechanical vibration damping apparatus cannot satisfactorily oppose a full spectrum of vibrations which are likely to develop at different rotational speeds of the engine and/or under different loads and/or on different types of terrain and/or in different types of motor vehicles. The same applies for the reduction of noise under such widely different circumstances. The bulk and cost of mechanical vibration damping apparatus increase considerably if such apparatus are to be designed with a view to satisfactorily oppose vibrations and to reduce noise under two or more different circumstances which require different modes of vibration damping and/or different modes of noise reduction. Another drawback of purely mechanical vibration damping apparatus is that they cannot conform their damping characteristics to a variety of widely different operating conditions which vary within wide ranges (for example, to different operating conditions which arise as a result of acceleration of the engine-driven flywheel from a relatively low speed to a much higher speed or vice versa). One of the reasons for such lack of versatility of mechanical vibration damping apparatus is that the histeresis of their energy storing elements which act in the circumferential direction of the flywheels cannot adequately conform to changing operating conditions. Moreover, mechanical vibration damping apparatus are prone to malfunction and their parts are subject to extensive wear.
Another drawback of presently known vibration damping apparatus is that they do not allow for extensive angular movements of the flywheels relative to each other. In other words, the damping action of the damper or dampers must be very pronounced, at least during the major part of the extent of angular displacement of the flywheels relative to each other. This prevents the conventional apparatus from effectively damping large-amplitude vibrations.